The present invention is directed to office or executive chairs and more particularly to office chairs which swivel about a vertical column and in which the backrest is articulated to the seat portion so as to be selectively tiltable or reclinable with respect to the seat, which seat synchronously moves forwardly as the backrest tilts rearwardly. The seat may also be raised or lowered by a gas cylinder.
Contemporary chair designers strive for combining the primary characteristics of both esthetics and comfort. As a result various approaches to office or executive chairs have resulted in many different designs. In most designs the seat and back are fixed and tilt together. In other designs the seat is fixed and the back alone tilts. A few designs attempt to achieve a higher degree of comfort by so connecting the seat and backrest that the seat is caused to slide forwardly in a prescribed path responsive to the tilting of the backrest. This is sometimes referred to as "synchronous" seat and back adjustment. The object is to adjust the seat position and inclination automatically as the backrest is tilted to various angles. Once the desired backrest angle is reached the seat and back are locked in position. The goal of the designer is to so reposition the seat responsive to the tilt of the backrest that the maximum comfort level is achieved.
It is another object of the furniture designer, which should not be overlooked, to achieve a pleasing esthetic effect in the furniture while accomplishing his comfort goals. Even further, as a third consideration, the designer is looking for a furniture design which is "manufacturable."
Examples of prior approaches to the "synchronous" seating concept known to the applicants include:
(1) A United States patent to Uneo No. 4,045,081. In the reclining chair described by Uneo, as the upper portion of the backrest is tilted rearwardly, the seat member not only shifts forwardly, but because of the articulated connection between the backrest and seat, the seat, sometimes referred to as the "seat pan," is actually raised after the backrest has pivoted slightly. This results because the articulated connection is forward of the backrest pivot point, and thus as tilting continues, the articulated connection begins to rise. This lifting of the seat pan causes the hips and buttocks of the occupant to tend to slide forwardly, which is not conducive to comfort.
(2) In a British patent to Scott No. GB 2041735, there is described an office chair in which the backrest pivots about an axis located above the seat pan and the seat pan slides forwardly in synchronization with the rearward pivoting of the backrest. Again because of the horizontal relationship between the pivot point and the articulated connection between the seat and backrest, the seat pan tends to rise as it moves forwardly resulting in the aforedescribed uncomfortable effect.
(3) An initial effort to overcome the problem realized by the Uneo and Scott patents described hereinabove is disclosed in a German patent to Vogtherr (one of the joint inventors in the present application), No. DE 3313677. In this patent, an attempt is made to suspend the chair in such a manner that when the backrest is tilted rearwardly, the seat or seat pan actually tends to lower as it slides forwardly. This is believed to provide a more comfortable result. Because of the suspension system disclosed in the Vogtherr patent, the center of gravity of a person remains substantially undisturbed during the tilting of the backrest. While the Vogtherr approach is theoretically sound, there are some practical problems in reducing this theoretical approach to a manufacturable piece of furniture. These problems include the fact that the suspension described in the Vogtherr patent tends to place stress on the support system as the pivot point (and center of gravity of the occupied chair) is horizontally displaced from the point of support by a substantial distance; a relatively strong locking system (approximately 800 newtons) is required to fix the seat in a prescribed inclined position; the esthetic appearance of the area beneath the seat tends to be "cluttered"; and the seat design is not adapted for easily varying the width dimension thereof.
With the aforesaid considerations in mind, the present invention adopts the general concept of synchronous seating as described in the German patent to Vogtherr in which the point of articulation between the backrest and the seat is caused to move downwardly as the backrest is tilted rearwardly. However, the present invention includes changes and additional features which cooperate to overcome the significant manufacturing problems realized by the earlier Vogtherr design. For instance, the support system of the present invention utilizes a unique supporting frame which features a transverse primary support arm aligned with and mounted atop the vertical support column which, in turn, adjustably connects the chair to the base through a gas cylinder. The aforesaid transverse support arm primarily supports the seat and backrest assembly along a transverse support axis substantially underlying the center of gravity of the occupied chair. This provides several advantages. First of all, the stresses on the support system are significantly reduced; the frictional force necessary to lock the chair in a prescribed position is minimized; the simple underneath structural appearance is maintained; and all of the chair controls are incorporated in the transverse support arm and are more easily accessible to the occupant of the chair.
The support frame is provided with a forward cross arm that supports a sliding/locking member in position to operatively engage a pair of laterally spaced, inwardly facing slotted housings in which the sliding/locking member moves. The sliding/locking member is rotatable between a first sliding position and a second locking position with the opposed slots. The sliding/locking member is of a non-circular cross section. In the first or sliding position the greater dimension of the sliding/locking member is aligned with the direction of movement, while in the second or locking position the greater dimension of the sliding/locking member is moved into frictional gripping relationship between the walls of the housing forming the slotted opening. While this type of locking system is capable of resisting a dislodging force of only approximately 200 newtons because of the unique suspension system described hereinabove, this is quite adequate to securely lock the chair at a prescribed position.
In order to connect the support frame to the backrest/seat assembly, the support structure of the present invention further includes a pair of laterally spaced side arms affixed at their lower ends to the opposed ends of the aforementioned transverse support arm. The side arms extend upwardly from the transverse support arm, then rearwardly terminating at a pivotal support point generally adjacent the lumbar region of the backrest. The backrest is pivotally connected between the terminal ends of the side arms at the aforesaid pivotal support point. The backrest is curved from top to bottom and from side to side for purposes to be described hereinafter.
The side arms may take the form of either of two configurations. In the first configuration, the side arms are a full length, in which case each side arm extends upwardly, angling forwardly from the cross arm, then rearwardly to the terminal point. In the second configuration, which is in reality a shortened arm rest for secretaries and typists, the side arms merely extend vertically then rearwardly for a shorter distance.
A separable connector or mounting receptacle is seated within the central portion of the transverse support arm of the support system to receive the upper end of the gas cylinder. The connector serves the purpose of retaining the gas cylinder actuator and the locking linkage in place, while also providing a seat for the rear end of the tension spring tongue. Because of the separable connector, the support frame may be more easily and economically manufactured, since a variety of sizes and shapes of support frames can all be made to utilize the same type of connector.
Another unique feature of the present invention resides in a removable decorative foot cap which snaps into place on the extremity of each leg of the support base. The decorative foot cap allows for easily changing colors, shapes, and for replacing worn or unsightly foot caps.
It is therefore an object of the present invention to provide an improved support structure for office chairs of the type having a synchronous seat and backrest adjustment feature.
Another object of the present invention is to provide a support structure of the type described in which the moment arm between the center of gravity of the occupied seat and the main support member is minimized.
A further object of the present invention is to provide an effective and simple locking technique for use in conjunction with the support system of the type described.
Yet another object of the present invention is to provide a support or suspension system for a chair of the type described and a locking system, which systems are so related that a very slight locking pressure (on the order of 200 newtons) is sufficient to maintain the seat in a stationary position.
Still another object of the present invention is to provide an office chair of the type described in which the backrest is curved from top to bottom and from side to side to maximize the horizontal displacement between the articulated connection and the axis about which the backrest pivots.
Another objectof the present invention is to provide a support system of the type described in which the transverse support member is extendable for use in wider seat configurations.
Finally, an object of the present invention is to provide an office chair of the type described having replaceable decorative foot caps on the legs of the base thereof.